CVE Watch—

CVE-2025-66376

Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability

CVSS

—

No CVSS

EPSS

12.0%

p96

KEV

YES

Mar 18, 2026

Exploit Today

0-100

Published: — · Last modified: —

EPSS · 30d

12.0%EPSS · 30 days12.0%

2026-06-302026-07-16

KEV catalog record

Product

Synacor / Zimbra Collaboration Suite (ZCS)

Vulnerability

Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability

Added to KEV

Mar 18, 2026

Remediate by

Apr 1, 2026

Known ransomware use

Summary description

Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability in the Classic UI where attackers could abuse Cascading Style Sheets (CSS) @import directives in email HTML.

Required action

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Notes

https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories ; https://nvd.nist.gov/vuln/detail/CVE-2025-66376

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